PS: the links I gave are meant to be helpful, but not to imply in any way that this is a bad question. Can you give some examples of the situations where you're running into this, and what you've tried?
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mattdmSep 1 '11 at 2:26

4 Answers
4

Exposure is essentially controlled by Aperture, Shutter speed and ISO. You need to balance these to get correct exposure. Assuming you are shooting manual (M on the left top dial).

The delicate balance between aperture, speed and iso depends on the image you are trying to capture. I usually ask myself questions before taking a picture.

Do i need to isolate subject from background?

Do i need to include background in the picture?

Do i care about about background?

If i can answer the above questions then it fixes aperture for me.

Do i need to capture motion?

Is subject moving and i want to freeze action?

This fixes speed for me.

Once one of speed and aperture is fixed then look at your light meter. Change the other till the meter indicates correct exposure. There are limitations to be considered. Like you don't want speed to be very low etc. And then ISO comes into picture. A stop change in one these cuts light by half or increases twice.

Usually you control your exposure using aperture, shutter speed, and ISO; too much light is not usually a problem, because you can find an acceptable combination of the above to give the proper exposure even in the most intense sunlight. Most people have the opposite problem, too little light.

Sometimes for artistic reasons you can't adjust one of those parameters into submission. One common example is using a very long shutter time to get a smooth water effect for a waterfall. In that case you can use a neutral density filter to cut the amount of light coming into the camera.

If I understand your question properly, there are a few ways to account for too much light when exposing a scene. First off, you can always try increasing shutter speed, or reducing aperture. Additionally, you should choose the lowest ISO setting (or film) that you can.

There may be occasions, however, when reducing shutter speed or tightening aperture will not serve your needs. Such cases may be when you need a very thin depth of field, or need a longer shutter speed to allow objects in motion to blur, etc. When you have limits on what settings you can use for aperture and/or shutter, you can always try some neutral density filtration. A neutral density filter is a semi-translucent filter that reduces the amount of light entering the lens. They usually come in various grades, anywhere from 1 stop to as much as 10 stops or so. This grading is how much light they reduce...so a 1-stop ND filter will allow you to expose one stop greater (wider aperture or longer shutter). With more expensive filtration systems, you can often stack multiple ND filters to add a LOT of filtration...one could, say, stack a 1-, 2-, and 3-stop filter for a total of 6 stops of filtration total.

Better filtration systems also provide the ability to use graduated ND filters...or filters that are rectangular, fully translucent on one end, and partially opaque on the other end, with a gradient transition in the middle. Such filters also come in various stops like their solid ND cousins. They are often very helpful in re-balancing the amount of light in a divided scene, such as a landscape. When the sky is particularly bright and the landscape is shaded, the total dynamic range of a scene may be far greater than a camera is capable of capturing in a single shot. With graduated ND filtration, you can filter the sky, without affecting the landscape, thereby reducing the dynamic range of the scene such that a camera CAN capture it without overexposure.

I highly recommend looking into Lee and Cokin filtration systems. Both offer advanced filtration systems with an extensive variety of neutral and colored solid and graduated filters.